Field of Invention
The present invention relates to a system for tracking of the position of multiple objects utilizing radio frequency (RF) transmitters, and more specifically to a highly accurate system for tracking the position of multiple objects that may be implemented indoors.
Description of Related Art
Determining the position of an electronic device or object has been a subject of much research since the emergence of RADAR and SONAR. A variety of proximity and position detection schemes exists today. For example, the Global Positioning System (GPS) has been transformational to military and civilian users by providing a system of orbiting satellites that have highly synchronized clocks emitting timing information continuously. A GPS receiver obtaining signals from three satellites can triangulate its position with time of receipt information. This triangulation is accurate to meters and is highly suitable for use in navigation for oceanic ships, cars or when walking. However, GPS signals do not provide accuracy to five inches or less as would be desirable in a Virtual Reality (VR) and Augmented Reality (AR) systems. VR technologies simulate an environment and typically provide a view of this environment on a head mounted display (HMD) which may also provide headphones with synthesized sound. AR technologies provide images which are partially of actual object with synthesized computer generated images superimposed upon it. VR and AR technologies are described in U.S. patent application Ser. No. 13/967,058 filed Aug. 14, 2013, issued as U.S. Pat. No. 9,519,344 on Dec. 13, 2016, and Ser. No. 14/614,734 filed Feb. 5, 2015, issued as U.S. Pat. No. 10,200,819 on Feb. 15, 2019, owned by the owner of this application, and are hereby incorporated by reference as if set forth in their entirety herein.
GPS systems do not work as well indoors. Many indoor tracking systems have been proposed. Apple iBeacons, for example, use Bluetooth Low Energy (BLE) transceivers to transmit beacon identification (and other) information and the location of a receiver from the iBeacon is calculated based on Received Signal Strength Indicator (RSSI). Such a system is a proximity indicator, and does not provide a high level of location accuracy necessary in many modern applications. There have been other attempts at accurate indoor wireless positioning systems, including for example the IEEE paper “Improving WLAN-Based Indoor Mobile Positioning Using Sparsity”, by Pourhomayoun and Fowler (2012). However, to date, such systems have accuracy of about a meter, which is not adequate for real time tracking of position in many applications.
The above tracking systems have multiple uses in gross position determination. However, more recently, the need has arisen for precise location and tracking of objects or devices, both indoors and outdoors. Wireless tracking is described more fully in U.S. patent application Ser. No. 14/600,025 filed Jan. 20, 2015, published on May 14, 2015 as U.S. Pub. No. US 2015-0130664 A1, and Ser. No. 14/354,833 filed Apr. 28, 2014, issued as U.S. Pat. No. 9,945,940 on Apr. 17, 2018, owned by the owner of the this application and are hereby incorporated by reference as if set forth in their entirety in this application. For example, VR and AR technologies are starting to emerge as viable interactive means of communicating, working, playing, and exploring with the digital world. To make these new AR and VR systems more effective, the need for improved accuracy and faster response in these systems increases. These improved systems must contemplate the user experience from the moment they begin interacting with the ARlVR system, thru its use and return to a disconnected world. Such an immersive experience requires precise real time tracking of the user for a realistic experience.
U.S. Pat. No. 8,749,433 issued Jun. 10, 2014, discusses a system for tracking an RF transmitter. If attached to an object, tracking this RF transmitter will also track the attached object.
This type of tracking has been integrated into a virtual reality system as discussed in U.S. patent application Ser. No. 14/614,734, filed Feb. 5, 2015, issued as U.S. Pat. No. 10,200,819 on Feb. 15, 2019, owned by the owner of this application, and hereby incorporated by reference in its entirety herein. In such a system, a transmitter transmits its location, and multiple receiver antennae and a controller use time difference of arrival (TDOA) to determine the position of the transmitting device. This allows the tracking to be precise; however, if only one transmitter is utilized, then only one transmitter (point) may be tracked.
Another technique for internal tracking of objects is described in the paper “Multifrequency-Based Range Estimation of RFID Tags” (2009, IEEE, by Xin Li). In this paper, multiple frequencies are compared using a phase difference of arrival (PDOA) to locate or track objects. The radiofrequency identification (RFID) tags employed with the present system include a means for transmitting and receiving RF signals, a processor, memory which may include executable code and possibly sensors. The RFID tag can then execute a program and function as described herein.
In this technique, multiple frequencies are transmitted to an RFID, which retransmits the frequencies as is known to those skilled in the art. The returned signal can be used to calculate the distance from the transmitter to the RFID. However, analysis of the returned signal only provides a distance measurement from the transmitter to the RFID tag. Several tags must be used to determine directionality.
Of particular interest in AR and VR are virtual reality glasses and/or head mounted displays (“HMDs”). As HMDs become more prevalent, new functionality to enable better engagement with and connection to the virtual world become critical.
There are a variety of approaches that attempt to provide an intuitive interface for controlling content shown on these devices—as is critical to the effectiveness of how HMDs are used. As most of these HMDs will be wireless and mobile, operated away from desks or related environments where computer mouse or trackpads are accessible, there needs to be an effective solution for providing input control without requiring a typical input device. Cameras can be installed on the HMDs to track a person's hand gestures and these gestures can then be used for interaction. But, in these camera-based systems, gesture tracking can be limited by the field of view of the camera, accuracy of the camera gesture tracking, range detection of the hand position as viewed by HMD cameras, or the lack of tactile input to the hand or fingers as they are interacting with the program running on the HMD.
Most VR/AR systems require recalibration of the tracking system when the number of tracked objects changes. This make the systems difficult to properly configure and impractical for certain uses.
The geographic area in which objects may be tracked is typically limited. The objects must be within the transmission range of the transmitters. Once the objects are outside of this area, they can no longer be tracked.
Some prior art tracking systems require significant RF transmission that require significant energy to operate. If a user would like to continuously track objects, then the amount of power dissipation becomes significant. This power dissipation reduces battery life.
Barcode readers and mobile scanners are described in U.S. patent application Ser. No. 14/568,468 filed Dec. 12, 2014 which is owned by the owner of this application and hereby incorporated by reference as if set forth in its entirety herein.
While the above systems for tracking are useful, they do not provide a suitable method of tracking objects with precision and in real time. Furthermore, they do not address real time tracking of multiple objects in a coordinated way as would be required in an AR or VR environment. Currently there is a need for highly accurate and low power tracking systems for indoor and outdoor tracking of multiple points on multiple objects.